1. Field of the Invention
One disclosed aspect of the embodiments relates to image processing methods and image processing apparatuses which may quantize input image data by an error diffusion method.
2. Description of the Related Art
In the past, quantization processing by an error diffusion method may diffuse an error caused by quantization of each pixel to a predetermined pixel in accordance with a two-dimensional error matrix, for example. An adjacent pixel to be processed on a same line is quantized by adding the error diffused to the original pixel value. After the pixels for one line have completely been quantized, pixels for one adjacent line are quantized in the same manner. Thus, all lines contained in image data are sequentially quantized.
Quantization processing by an error diffusion method is required to sequentially quantize pixel by pixel because a processing result from an immediately preceding pixel is used to process a pixel of interest, as described above. In other words, higher-speed quantization processing is difficult to achieve.
Accordingly, a method for achieving higher speed image processing by an error diffusion method has been proposed which processes two pixels simultaneously at one clock (see Japanese Patent Laid-Open No. 2010-050846).
However, according to the image processing method disclosed in Japanese Patent Laid-Open No. 2010-050846, it is unable to diffuse an error value of one pixel of four pixels to a close pixel. For that reason, the error data of the pixel may be diffused to a pixel away from the proper pixel. Diffusion of error data to a pixel away from a proper pixel may generate discontinuous fine lines and/or reduce the sharpness of an image part which should be highly sharp. In this way, a part of an algorithm of an error diffusion method in the past is changed at the expense image quality in order to increase the speed of image processing by the error diffusion method.